A safety razor is a shaving implement with a protective device positioned between the edge of the blade and the skin. The initial purpose of these protective devices was to reduce the level of skill needed for injury-free shaving, thereby reducing the reliance on professional barbers for providing that service and raising grooming standards.
The term safety razor was first used in U.S. Pat. No. 228,904 issued to Frederic and Otto Kampfe in 1880, for a razor in the basic contemporary configuration with a handle attached at right angles to a head in which a removable blade is placed.
Not much has changed in the innovation of the design of safety razors since King C. Gillette's U.S. Pat. No. 775,134 was issued in 1904. Gillette's innovation was a thin, cheap, double-edged blade that could be disposed of when dull. Gillette's blade holder clamped the blade between a backing and a guard plate that was then attached to a handle. The patented design also allowed for adjusting the gap between the blade and the guard plate to allow for light or heavy growth beards or to suit the skill or custom of the shaver.
The most popular modern shaving implement uses cartridge based razors that include a number of single-edged razors in a disposable cartridges. The consumer cost of these disposable cartridges is quite high and has been an impetus for the return to traditional wet shaving using double-edged safety razors. Refilling a traditional safety razor can cost under 10 cents whereas modern cartridges can cost well over $2 to replace. Today's modern razor cartridges can also irritate the skin more than needed due to the multiple blades.
The term “aggressiveness” is used with respect to traditional, non-cartridge based razors to refer to the subjective feeling and performance of the safety razor. Generally, more aggressive safety razors expose more of the razor blade to the skin and are suitable for a heavier beard as they will require less strokes. These more aggressive safety razors are also prone to more nicks, cuts and irritation, and require a more skilled hand. Less aggressive safety razors can be suitable for shorter stubble and beginners to safety razor shaving. Because a man's stubble can vary in length depending on the time from his last shave, it is desirable to have a safety razor that can provide different levels of aggressiveness.
The aggressiveness of a safety razor can be defined by a number of different factors, including, but not limited to, the exposure of the blade and the blade gap. The exposure of the blade is defined as the protrusion of the blade edge beyond a line tangent to the cap and the guard, and the blade gap is defined as the space between the blade edge and the guard. Other factors that can influence aggressiveness can include the weight of the razor head, overall razor weight balance between the handle and razor head, and the handle length.
Safety razor designs have often tried to provide some level of to adjust aggressiveness of the razor. Often, as in King C. Gillette's above patent, this is provided by some means to adjust the blade gap between the blade and the guard plate. Other examples of this type of adjustments include U.S. Pat. No. 284,880 to Schnitzler et al. and U.S. Pat. No. 2,700,817 to Erickson. Adjustment of the blade gap can allow for variance in stubble length but is only one factor affecting aggressiveness of a safety razor. Unintentionally changing the blade gap can change subjective aggressiveness of the safety razor significantly.
Blade angle is another factor that influences aggressiveness of a safety razor. The blade angle can be defined as the angle between the blade edge and a line tangent to the cap and guard. There is a preferable angle of about 30 degrees from the face, but this may vary based on the different beards, stubble length, skin type (i.e. likeliness of razor irritation), and even different areas of the same beard (e.g. neck versus face). Traditional double-edged safety razor designs typically have a fixed geometry for clamping the blade between the cap and guard plate that provides for a single static blade angle. Some single-edge razor designs have provided mechanical adjustment mechanisms that can be prone to failure or slippage, or that not translate to double-edged safety razors, such as that shown in U.S. Pat. No. 3,080,651 to La Cas.